GEO 100 Volcanoes

Stratovolcanoes- also known as ______________ -large, cone-shaped volcanoes with steeper slopes -made of alternating layers of lava, tephra, and debris -often symmetrical, but can be odd shapes from landslides, etc.

"composite volcanoes"

____________________________- higher SiO2 content increases viscosity; don't flow far from vent (remain close to vent)

Andesitic (INTERMEDIATE) lava flows

4. ____________________________ -fierce winds from a passing typhoon blew the ash in all directions before it "showed" down on nearby buildings *many roofs collapsed under the sheer weight, killing hundreds in their homes -ash clouds can also block the sun and lead to temporary global cooling

Annihilation from ash clouds

______________- angular rock fragments -angularity indicates the absence of rounding by transport -deposited relatively close to clast source (ex: talus under a cliff face)

Breccia

2. ____________________________ *as pyroclastic flows exploded, they melted the glaciers on the mountain--> 40 mph Lahar -Lahars- thick mixtures (think wet concrete) of mud & water that slide down slopes like an avalanche

Buried by fast-flowing mud

______________- rounded rock fragments -clasts rounded as flowing water wears off corners & edges -deposited farther from the source than breccia (ex: river channel)

Conglomerate

1. ____________________________ -Mount Vesuvius (a stratovolcano) erupted explosively, sending fast moving waves of super heated gas down the sides of the volcano as a pyroclastic flow (gas, ash, & rock) traveling up -effected two ancient roman cities: Pompeii & Herculaneum -This is arguably the most deadly volcanic event -can travel for miles and are impossible to outrun -produced by ____________________________ *suring eruption, the rock layer is smashed into tiny particles, which mix with hot ash and gases to form a giant mushroom cloud *the cloud then collapses and cascades down the side of the volcano as a pyroclastic flow

Cooked by super-hot waves of gas; explosive 'composite volcanoes'

Clastic sedimentary rocks consist of: 1. ______________ (loose clasts)- mineral grains & rock fragments 2. ______________

Detritus; cementing

Sedimentary rocks form at or near ______________

Earth's surface

Hot spot intersecting a MOR- ______________

Iceland

5. ____________________________- threats are mostly from ______________ lava -may completely destroy immovable objects -bigger threat to property than to people (rare to kill people)

Lava flows; basaltic

In 79 CE, the citizens of Pompeii in the Roman Empire were buried by pyroclastic debris derived from an eruption of ______________

Mt. Vesuvius

____________________________ provide the raw material for all sedimentary rocks

Physical & chemical weathering

______________- round blobs of basalt cooled underwater (common on mid-ocean ridge)

Pillow basalt

______________ is a dominant control on volcanism

Plate motion

____________________________- the highest level of SiO2--> makes it the most viscous lava

Rhyolitic (FELSIC) lava flows

______________- clastic rocks made of sand-sized particles -common in beach and dune settings -quartz is, by far, the most common mineral sandstones

Sandstone

3. ____________________________ -when a volcano sits beneath a lake, gases from the magma can filter up through cracks in the crust and become trapped under the water as carbon dioxide -______________ (ex: an earthquake/landslide) can cause the CO2 to rise rapidly to the surface of the lake -this rare but deadly event is called a ______________

Suffocated by poisonous gases; violent movement; limnic eruption

Which of the following is true concerning the 1980 eruptions of Mt. St. Helens?

The eruption began with a lateral blast of debris that was ejected extremely fast

6. ______________ -______________ eruptions can create giant waves (ex: Krakatau)

Tsunamis; island-arc

Crater- ____________________________ -form as erupted lava piles up around the vent -summit eruptions- located within the summit crater; flank eruptions- located on sides of volcano

a bowl-shaped depression atop a volcano

Caldera- ____________________________ -much LARGER than a crater -a magma chamber empties and the volcano collapses inward (ex: Crater Lake, OR)

a gigantic volcanic depression

Death Valley, CA shows a road that curves around a(n) ______________

alluvial fan

Mt. St. Helens eruption: -____________________________ -an initial vertical blast led to a ____________________________ *tore off the entire north side of the mountain

an earthquake-triggered landslide released pressure; much stronger lateral blast

A volcano is ____________________________

an erupting vent through which molten rock surfaces/a mountain built from magmatic eruptions (volcanoes are a clear result of tectonic activity and pose a number of hazards to humans)

Clast shape: - ______________- the degree of edge or corner smoothness -______________- the degree to which a clast nears a spherical shape *Well-rounded indicates long transport distances *Angular indicates negligible transport

angularity; sphericity

Pyroclastic flow- ____________________________ -can move hundreds of miles per hour; are immediately deadly to anything in their path (classic ex: Mt. Vesuvius- wiped out Roman city of Pompeii, 79 CE)

avalanches of hot ash that race downslopes

Protection from eruptions: -Reoccurrence interval- ____________________________ *Active- ____________________________ *Dormant- ____________________________ *Extinct- ____________________________ (tectonics can shut off magma; then erosion takes over)

average time between eruptions; erupting, recently erupted, or likely to erupt; hasn't erupted in hundreds to thousands of years; hot capable of erupting

Beach sediments travel ______________ the ocean during a transgression and ______________ the ocean during a regression

away from; toward

Pahoehoe-______________

basalt with a glassy, ropy texture (w/ flow, the skin is rolled into ropy ridges 7 furrows)

Style of gas escape controls eruption violence: Low viscosity (______________)- ____________________________ High viscosity (______________)- ____________________________

basalt; easy escape, mellow eruption rhyolite; difficult escape, violent release

Which environment would most likely produce sedimentary deposits characterized by very well-sorted, well-rounded grains that are nearly pure quartz?

beach

Geologists call individual layers of sedimentary rocks ______________, whereas several of them together are called ______________

beds; strata

Shield volcanoes- ____________________________ -constructed by lateral flow of low-viscosity basaltic lava -have a low slope and cover large geographic area (ex: Mauna Loa, HI)

broad, slightly dome-shaped

Scientists monitor volcanoes to help predict when eruptions will occur. Which of the following is NOT a potential sign to look for when predicting volcanic eruption?

changes in Earth's magnetic field

Precipitation of gypsum due to evaporation of seawater produces which kind of sedimentary rock?

chemical

Of the primary forms of subaerial volcanoes, ______________consist of a simple pile of tephra often formed in a single eruption

cinder cones

Most important diagnostic for clastic rocks: ______________- the diameter of fragments or grains

clastic size

What type of sediment is typically food in lake bottoms?

clay/mud

Which of the following is NOT true? Sediments deposited in a beach environment are typically ______________

composed of angular grains

Geologists also distinguish sedimentary rocks by ______________ -Siliceous-______________ -Argillaceous- clay-rich -______________- contain calcite or dolomite

composition; quartz-rich; carbonate

Lava tubes- ______________

conduits for basaltic lava

Cinder cone- ____________________________ -the smallest type of volcano -built of ejected lapilli-sized fragments piled up at a vent -often symmetrical with a deep summit crater

conical piles of tephra

Pele's hair ______________

consists of thin strands of basaltic glass

Basaltic lavas ______________

contain more iron and magnesium than rhyolitic lavas

Rhyolitic lavas ______________

do not flow as far from the vent as basaltic lavas do

Warning signs indicate that an eruption is imminent: -______________ -heat flow -______________ -emission increases

earthquake activity; changes in shape

Nonviolent eruptions characterized by extensive flows of basaltic lava are termed ______________

effusive

Eruptive style- two dominant styles: -______________ eruptions produce ____________________________ *lava flows stream away from vents *lava lakes can from near, or inside the vent. Lava fountains can reach up to 500 m high *common with mafic magma (basalt) -______________ eruptions ______________ *high gas pressure is from more viscous SiO2-rich magma *create pyroclastic debris and cover land with tephra *mostly andesitic and rhyolitic compositions

effusive; lava flows, a vast outpouring of lava; explosive; release pressure catastrophically

Magma composition controls gas content: ______________ magmas have more gas; ______________ magmas have less

felsic; mafic

The cloud that rises from the vent of an actively erupting volcano is composed ______________

fine volcaniclastic debris (ash) suspended in the air

Diverting flows- ____________________________

flowing lava can be diverted

Volcanic soils are ______________ fertile; excellent for crops

highly

Basaltic (MAFIC) lava- very ______________, ______________, and ______________; are often thin and fluid- effusive eruptions and flow rapidly for long distances

hot; low silica; low viscosity

A fast-moving flow consisting of a mixture of water and volcaniclastic debris is termed a ______________

lahar

Volcanoes often erupt ______________ of fragments

large quantities

Rhyolitic lava rarely flows- rather, lava plugs the vent as a ______________

lava dome

______________- lava can be thin and runny, or thick and sticky

lava flows

Pyroclastic debris from basaltic eruptions- ____________________________ (bombs, blocks, Pele's hair, Pele's tears)

lava fragments that freeze mid-air

-Sedimentary rocks form ______________, which record a history of ____________________________ and only occur in the upper part of the crust -Sedimentary rocks cover underlying basement rock

layers; ancient environments

Composition and cementation of grains occurs during the stage of clastic sedimentary rock formation called ______________

lithification

Four classes of sedimentary rock: 1. Clastic- ____________________________ 2. ______________- cemented shells of organisms 3. Organic- ____________________________ 4. ______________- minerals that crystallize directly from water

loose rock fragments (clasts) cemented together; biochemical; carbon-rich remains of Ince living organisms; chemical

What properties of the source magma lead to the formation of a shield volcano?

low viscosity and mafic composition

Compared to felsic lavas mafic lavas have a ______________

lower viscosity

Volcanic architecture- volcanoes come in many shapes and sizes -the shape and size are governed by ______________

magma type

Swamps, channels, floodplains, and submarine slopes all play a role in the development of ______________

marine debris

The products of volcanic eruptions come in three forms: 1. Lava flows- ____________________________ 2. ____________________________- fragments blown out of a volcano 3. Volcanic gases- ____________________________

molten rock that moves over the ground; pyroclastic debris; expelled vapor and aerosols

Volcanic activity is evident on the ______________ and ______________

moon; planets

The textural term for a basaltic lava flow that has a smooth, ropy appearance is ______________

pahoehoe

The primary difference between breccia and conglomerate is that conglomerate ______________

possess more rounded grains than breccia

Explosive eruptions that generate debris: ______________- "frothy" volcanic glass (lots of open space) ______________- fragments of volcanic glass that are less than 2 mm in diameter ______________- angular pumice fragments

pumice; ash; pumice lapilli

A mixture of air, hot ash, and pumice lapilli that rushes down the side of a volcano in a scalding avalanche is termed a(n) ______________

pyroclastic flow

Which of the following poses the greatest hazard to human life associated with volcanoes

pyroclastic flows

Well-sorted sediments with grain sizes falling in between 1/16 mm and 2mm, later cemented together and lithified becomes the clastic sedimentary rock named ______________

sandstone

Limestone is most likely formed in which of the following environments?

shallow-marine carbonate

Of the three primary forms of subaerial volcanoes, ______________ are typically the largest in area

shield volcanoes

Of the three primary forms of subaerial volcanoes, ______________ have the most gently sloping sides, due to the low viscosity of the basaltic lavas that form them

shield volcanoes

Fine clastics-- composed of silt and clay -silt-sized sediments are lithified to form ______________ -clay-sized particles form ______________ or ______________ -fine clastics are deposited in ______________ (ex: floodplains, lagoons, mudflats, deltas, deep-water basins; often accompanied by organic matter)

siltstone; mudstone; shale; quiet water settings

Biochemical limestones are dominated by carbonate mud and fragments of ______________

skeletons of marine invertebrates made of calcite and aragonite

Columnar jointing-______________

solidified flows may contract, creating vertical fractures that are hexagonal in cross-section (ex: Devil's Postpile)

A'a'-______________

solidifies with a jagged. sharp, angular texture (w/flow, lava crumbles into shards & fragments)

Mt. Fuji in Japan is an example of a ______________

stratovolcano

Volcanic types are linked to ______________ -____________________________ oceanic crust covers 70% of Earth *recognizable basalt "pillows" (basalt erupted from fissures quenches as pillows) -most volcanoes form at ______________ *volatiles from subducting plate initiate melting on the overriding plate -continental rifts- man volcano types -oceanic hot spot- ____________________________ (ex: Hawaii) -continental hot spot- ____________________________ (ex: Yellowstone)--> also called "supervolcano"

tectonic plates; MOR generated; convergent boundaries; a plume under an oceanic plate; up through a continental plate

Pyroclastic deposits: ______________- deposits of pyroclastic debris of any size Tuff- ____________________________- can be deposited hundreds to thousands of miles away from the volcanic source

tephra; lithified ash

Clastic rocks are classified basis of ______________ and ______________

texture; composition

Clast composition- ____________________________ *yields clues about the original source rock; variety hints at transport processes

the mineral makeup of sediments

Sorting- ____________________________ -______________- all clasts have nearly the same grain size -______________- clasts show a wide variety of grain sizes - Degree of sorting ______________ with transport distance (nature of cement- minerals that fill sediment pores; quartz [SiO2] and calcite [CaCO3] are the most common cements) *All of the above provide clues about ______________ and ______________

the uniformity of grain size; well-sorted; poorly sorted; the source area; depositional

Sea level rises locally, and marine sediments are deposited on top of terrestrial sediments during events termed ______________

transgression

Grains become rounded primarily during ______________

transportation

"Pillows" formed ______________

underwater at a mid-ocean ridge

Clastic rocks: -Range from ____________________________ -As transport distance increases, sediment grain size ______________ *Gravel- coarse-grained sediment (boulder, cobbles, pebbles) *Sand *Mud- fine-grained (silt & clay)

very coarse to very fine; decreases

Gas bubbles in rock are called ______________

vesicles

Style of flow depends on ______________, which depends upon: -______________(especially SiO2, Fe, and Mg content) -______________ -______________ -______________

viscosity; composition; temperature; gas content (volatiles); crystal content

More ______________ magmas and more ______________ (rhyolitic lava flows-also makes these volcanoes more prone to explode)

viscous; volcanic gases

If a geologist found preserved mud cracks, he/she could conclude that the environment in which they formed ______________

was once covered in wet mud

Symmetric ripples form when ______________

water deposits sediment in layers, but the direction of flow periodically changes

Gases that are abundantly emitted by volcanoes include ______________

water vapor, carbon dioxide, and sulfur dioxide

The breakdown of exposed rock into small fragments and dissolved ions is termed ______________ and the removal of detritus from weathered rock at an outcrop is termed ______________

weathering; erosion

Clastic sedimentary rocks are create d by: 1. ______________- generation of detritus via rock disintegration *2. ______________- removal of sediment grains from parent rock *3. ______________- dispersal by gravity, wind, water, and ice 4. ______________- settling out of the transporting fluid 5. ______________- transformation into solid rock *compaction- burial adds pressure to sediment (squeezes out air & water ; compresses sediment grains) *cementation- minerals grow in pore spaces (precipitate from groundwater between pore spaces & "glue" sediments together

weathering; erosion; transportation; deposition; lithification

It is unusual for ______________ to carry grains larger than sand

wind